IGF-DES

IGF-DES is a naturally occurring, truncated form of insulin-like growth factor 1 (IGF-1). It was first characterized from human fetal brain (Sara et al., 1986) and from bovine colostrum (Francis et al., 1986; Francis et al., 1988), where it is thought to arise from post-translational cleavage of IGF-1. Structurally it is a 67-residue variant corresponding to residues 4-70 of mature human IGF-1, with the N-terminal Gly-Pro-Glu tripeptide absent; the three intramolecular disulfide bonds of the parent protein are retained. No high-resolution structure of the truncated variant itself has been reported, so structural work references the parent IGF-1 - the nuclear-magnetic-resonance solution-structure study of Cooke et al. (1991) is the standard structural reference, and the relationship between the variant and the full-length parent is described in structural and binding terms rather than treated as identical.

The defining research theme is how N-terminal truncation alters interaction with the IGF-binding proteins (IGFBPs). Receptor-binding and competition studies examined IGF-DES alongside full-length IGF-1, characterizing its interaction with the IGFBPs relative to its binding at the type-1 IGF receptor (Carlsson-Skwirut et al., 1989; Ross et al., 1989). Szabo et al. (1988) examined a purified IGFBP and the role of the IGF-1 N-terminal tripeptide in its binding. Heding et al. (1996) applied biosensor (surface-plasmon-resonance) kinetics to characterize the interaction of IGF-DES with IGF-binding-protein-3, and Francis et al. (1992) compared a panel of N-terminal IGF-1 analogues, including IGF-DES, in binding-protein-secreting cell lines. Structure-function work by Bagley et al. (1989) mapped the contribution of the IGF-1 N-terminal region, examining how stepwise removal of the first residues - and the loss of Glu3 in particular - relates to receptor binding in a myoblast system.

The L6 rat myoblast protein-synthesis bioassay is the foundational in-vitro system in which IGF-DES was first characterized (Ballard et al., 1987), and the molecule recurs there as an IGFBP-resistant comparator to full-length IGF-1. DNA-synthesis assays in fetal rat brain cells were used to compare intact and truncated recombinant IGF-1 (Carlsson-Skwirut et al., 1989). Across the broader literature the reported cell systems include L6 and C2C12 myoblasts, H35 hepatoma cells, MCF-7 breast-carcinoma cells, BALB/c 3T3 and primary fibroblasts, and fetal-brain cells, where IGF-DES has been used to probe how IGFBPs modulate receptor-level signaling. Downstream IGF-1R signaling in these contexts is described through the PI3K/Akt and MAPK/ERK cascades (general IGF-1R biology).

IGF-DES has been used as an IGFBP-resistant comparator to full-length IGF-1 across several rat catabolic-state model systems, with whole-body nitrogen balance as a common measurement endpoint. The model systems examined include streptozotocin-diabetic rats (Tomas et al., 1991), dexamethasone-treated rats (Tomas et al., 1992), dietary nitrogen restriction (Tomas et al., 1991), small-bowel / gut resection (Lemmey et al., 1991; Lemmey et al., 1994), and reduced renal mass via subtotal nephrectomy (Martin et al., 1991). The molecule was also examined in growth-hormone-deficient lit/lit mice (Gillespie et al., 1990). Across these reports IGF-DES is studied as a research tool rather than as a therapeutic candidate; the descriptions here cover the model systems and what was measured, not biological outcomes.

Taken together, the literature positions IGF-DES as the binding-protein-decoupled reference point of the IGF system. Study designs commonly pair it with full-length IGF-1 (which retains full IGFBP interaction) and with a separate IGFBP-resistant IGF-1 analogue so that observed differences can be attributed to binding-protein interaction versus receptor binding. This makes IGF-DES a recurring mechanistic control in IGF-system research, and reviews of the truncated variant (Ballard et al., 1996) summarize its origin, structure, and use in this comparator role.